1. Field of the Invention
The present invention is directed to a catalyst system, a process and silicone compositions.
2. Brief Description of Related Technology
Organosiloxane fluids having alkoxy groups which polymerize by reaction with moisture and groups which polymerize by free-radical processes are known [see U.S. Pat. No. 5,300,608 (Chu) and U.S. Pat. No. 5,663,269 (Chu), the disclosures of each of which are hereby expressly incorporated herein by reference]. As demands for ever-faster polymerizing materials have arisen, more reactive free radical polymerizing groups have been incorporated into the alkoxy group containing organosiloxanes. However, it has been found difficult to prepare organosiloxane compositions which contain reactive free-radical polymerizing groups, such as acryloxyalkyl groups, by reaction of a silanol with a dialkoxy or trialkoxy silane containing a reactive acryloxyalkyl group.
U.S. Pat. No. 5,300,608 (Chu) and U.S. Pat. No. 5,663,269 (Chu) disclose processes for capping silanol groups with alkoxy silanes containing groups with polymerizable double bonds by reaction of the silanol with an alkoxysilane in the presence of organo-lithium reagents. These processes provide capping of a major proportion of the silanol groups. However, oftentimes the organo-lithium reagents do not produce suitable capping when the alkoxy silane contains a reactive group, such as an acryloxyalkyl or allyl group.
U.S. Pat. No. 4,798,889 (Pleuddemann) refers to a method of stabilizing unsaturated organosilicones using hydroxylamines, and U.S. Pat. No. 4,912,239 (Bank) refers to an improvement in the method of preparing an alkoxysilane in the presence of hydroxylamine as a polymerization stabilizer. However, these methods refer to stabilizing organosilicones and alkoxysilicones once formed; they do not refer to catalyzing the process of capping silanol groups with alkoxysilanes containing groups with polymerizable double bonds.
Accordingly, it would be desirable to provide a catalyst system which is capable of end capping a major portion of the silanol groups by reaction with alkoxysilanes containing a highly reactive acryloxy group or allyl group.